Thermostats and other temperature control devices are utilized in residential and commercial environments to control and regulate the environmental conditions within a structure. For example, a thermostat control device can regulate the temperature and airflow provided by a residential or commercial heating, ventilation and air-conditioning (HVAC) system. HVAC systems typically have control circuits that are required to be powered by a National Electric Code (NEC) Class 2 power source with a corresponding circuit breaker or current limit protection circuit. In the event that a larger transformer (i.e., not in compliance with a Class 2 power source) or a circuit breaker is not provided in or with the HVAC system, an excessive and potentially dangerous current can be output from the HVAC system and brought into occupied spaces in a building via wiring to the Thermostat control device.
However, conventional thermostats typically do not address the issue of over current protection on control input/output wiring to an HVAC system. Instead, conventional thermostats depend on an external circuit breaker that may or may not be installed at the control transformer for the respective HVAC system to which the thermostat is connected. If present, a conventional external circuit breaker typically trips at twice the rated current and after a long one (1) second time constant, which allows heating of wires, contacts and traces of the thermostat. Conventional thermostats also typically do not address short period over current let through, retries or fault annunciation.
A thermostat sold under the brand name Site Controls by Siemens Industry, Inc., Building Technologies Division, has an over current protection circuit. However, that over current protection circuit breaks connectivity to control outputs based on detection of the over current by hardware components alone without management of the over current issues noted above.